1. Field of the Invention
The present invention relates to an inkjet recording apparatus and a method of controlling the apparatus, and more particularly to control of wiping performed while cleaning liquid is supplied to a discharge port surface of a recording head.
2. Description of the Related Art
An inkjet recording apparatus that forms an image by applying ink from discharge ports of a recording head onto a recording medium is a low-noise, non-impact recording apparatus. The recording apparatus has various advantages such as an ability of performing a recording operation with a high density at a high speed. However, the ink is discharged from extremely small discharge ports, and hence, extremely small ink droplets (mist) may be generated in addition to expected ink droplets. Also, discharged ink droplets are bounced, and hence, extremely small ink droplets may be generated. Such ink droplets (hereinafter, also referred to as contamination ink) may adhere to the discharge port surface of the recording head, which may disturb desired ink discharge. In light of the above situations, a typical inkjet recording apparatus employs a configuration that wipes off a discharge port surface of a recording head with a member such as a blade to remove contamination ink.
However, a currently available inkjet printer or the like tends to use ink having a high image fastness to increase a water-resistant property and a weather-resistant property of a recorded image. Hence, a simple wiping mechanism, such as one described above using the blade, may insufficiently remove the contamination ink. This is because an adhering force of the contamination ink to the discharge port surface of the recording head is increased as a result of the use of the ink having the high image fastness. As described above, a coloring material having a good fixing property to a recording medium is easily fixed to the discharge port surface of the recording head. Such a coloring material may have a contradiction such that when the image fastness is increased, the ink discharging performance is decreased.
U.S. Pat. No. 5,905,514 discloses a configuration as one of solutions for the problems. In particular, predetermined processing liquid (cleaning liquid) is supplied to a discharge port surface of a recording head via a blade (wiper), to dissolve contamination ink on the discharge port surface with the cleaning liquid, and to wipe off and remove the dissolved contamination ink. With the configuration disclosed in U.S. Pat. No. 5,905,514, the following advantages are expected to be provided. (1) A frictional resistance between the discharge port surface and the blade can be reduced when the discharge port surface is wiped off, thereby reducing wearing and deterioration of the discharge port surface. (2) The dried contamination ink on the discharge port surface can be dissolved. (3) The contamination ink on the discharge port surface can be easily moved. (4) A thin film of cleaning liquid can be formed on the discharge port surface.
With the above configuration, the ink discharging performance can be maintained in a good condition when recording with the recording head and cleaning of the discharge port surface are periodically performed at a relatively short interval.
However, when an intermission period of a recording operation is a long period, the contamination ink may be thickened on and fixed to the discharge port surface. Hence, the ink discharging performance may become defective and would not be recovered. The contamination ink is thickened on and fixed to the discharge port surface due to the following factors. The thin film of the cleaning liquid is not uniformly formed on the discharge port surface. Hence, when the contamination ink adheres to a portion without the cleaning liquid and is left for a long period, the contamination ink gradually becomes difficult to be dissolved. Also, when ink, which has been dissolved once with the cleaning liquid, is left on the discharge port surface for a long period, a part of an ink component may be separated and fixed to the discharge port surface.
In contrast, when a density of an ink component in liquid such as the contamination ink remaining on the discharge port surface is a predetermined density or lower, the ink discharge would not become defective although a long period elapses without a wiping operation with the blade. That is, although the recording apparatus is left without the wiping, the ink component can be removed from the discharge port surface. Accordingly, when the intermission period of the recording operation becomes long, the density of the ink component in the liquid remaining on the discharge port surface may be diluted to a predetermined density or lower. Then, it is considerable that when the recording operation enters the intermission period, cleaning is performed with an increased supplying amount of the cleaning liquid to the discharge port surface, so that the density of the ink component becomes the predetermined density or lower by a single supplement of the cleaning liquid. However, if the recording operation is activated in a short time after the cleaning, the amount of the cleaning liquid used in the cleaning may be excessive. This configuration may increase a consumption amount of the cleaning liquid. Also, when dilution progresses step by step through a plurality of times of the cleaning, dilution unevenness within the discharge port surface can be reduced as compared with the case where the larger amount of the cleaning liquid is supplied by a single cleaning operation to provide an equivalent dilution. Further, a large consumption of the cleaning liquid may cause the following problems. In particular, a total amount of the cleaning liquid to be housed in the recording apparatus may be increased, the cleaning liquid may be scattered during the wiping operation, and an amount of contamination liquid to be collected from the discharge port surface may be increased.